SS8 Mr. Galbraith on the Velocity of Sound. 



Dr. Moll observes, page 425, was " annihilated," — we have, 



(105-9518 + 2-2U7)(l+^|^^^^|^)(3-1314.3 + 0-00105) = 



108-1665 X 1-0023 x 3-13248 = 339-622 metres. 



Experiment gives 340-06 



Error of formula —0-438 metre. 



In like manner if we compare 14 shots at each end of the 

 base, or 28 at both, fired on the 28th of June 1823, we have, 

 108-17742 X 1-00212 x 3-13248 = 339-582 metres. 

 Experiment gives 339*34 



Error of formula + 0-242 metre. 



Whence, these errors being of different signs, we may con- 

 clude that it is probable the formula agrees very well with 

 Dr. Moll's experiments, as the mean error of the whole would 

 only be about — 0-196 of a metre, or about eight English 

 inches ; a degree of coincidence, in such researches, not to be 

 expected. 



Though Dr. Moll has not stated the effect of the wind, yet 

 it may, I think, be inferred from his observations made at 

 each end of the base alternately, as on the 25th and 26th of 

 June 1823. 



On the first day, the velocity was 337-39 metres. 



On the second 346-59 



Difference 9-20 metres, 



or about 30 English feet. 



The same conclusion may be drawn from his experiments 

 when the guns were fired, and heard at both stations. 



Thus on the 27th of June 1823, Phil. Trans. 1824, p. 445, 



The mean of the one column II. is — — — = . . 52'-835 



The mean of column III. is . . . -^^^^ = • • 51^-04^9 

 Difference in time is 1 "786 



Now, ^-, „^- = 334-424 metres, 



^ J 17669'"-28 o.^.io^ 



And, -^3:549- =11^11* 



Difference. . = 11-700 metres, or about 38 English 

 feet per second, according as the velocity is determined from 

 the one end of the base, or the other. 



Now for want of other evidence, we may reasonably sup- 

 pose that this is occasioned by the effect of the wind accele- 

 rating the sound in the one case, and retarding it in the other. 

 Direct experiments are, however, still wanting to settle this 

 point in an unobjectionable manner, though from the state to 



which 



